As is well known, taximeters are utilized for fare tariff computations in rented vehicles by means of a multiplication of trip distances, which are covered, and time units, by prices, of a locally fixed tariff standard. The calculated price units are added and are indicated on a suitable display screen. The quantity of the hiring instances, trip price, distances covered with or without paying passengers, surcharge revenues, and the like, are stored for purposes of fare collection. The last-mentioned data, as well as the computation processes, have to be preserved, or the processes have to be performable also in the case of a failure of the current supply of the vehicle, contact interruptions, which are caused by shocks or corrosion, and also in cases of current supply gaps which may occur during operation of the vehicle, such as, for instance, in a cold start of diesel vehicles. In this regard, taximeters must be equipped with a buffer battery, in order to largely exclude manipulations and short-circuits, which is provided so as to allocate a buffer battery directly to the circuit board of the typically single board computer of the taximeter, and to solder it thereto.
With this concept, it is also unnecessary to provide a special battery compartment in the taximeter, which must be additionally lead-sealed and which requires more space than the direct attachment of the battery, upon the printed circuit board. The concept is thus meant to accommodate the requirement that a taximeter is to have an easy-to-read display which must be recognizable with one glance and, thus, as large a display field as possible and that the external shape of taximeters is to be constructed in such a manner that they permit an aesthetic integration into the dashboard. These contradictory requirements, which an installable taximeter has to meet, require an extensive utilization of the front wall or the front surface of the taximeter by the display and actuation means, by the model identification plate, and by means for parametric and diagnostic purposes which should be accessible from the front without having to remove the taximeter.
With the arrangement of the buffer battery upon the circuit board, if one has to put up with the circumstance that the charging capacity, and the space requirement, for the printed circuit board, must be selected to be so large, the amount of current consumption existing with the taximeter not being installed must be supplied by the buffer battery over a period of several years. Further, in this concept, a replacement of the battery by unsoldering and by resoldering is cumbersome and expensive and, in the case of insufficient care, it is not devoid of danger for the construction elements in its vicinity.